Cisco Security Advisory

Advisory ID: cisco-sa-20100120-xr-ssh

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20100120-xr-ssh

Revision 1.0

For Public Release 2010 January 20 16:00  UTC (GMT)

Summary

The SSH server implementation in Cisco IOS XR Software contains a vulnerability that an unauthenticated, remote user could exploit to cause a denial of service condition.

An attacker could trigger this vulnerability by sending a crafted SSH version 2 packet that may cause a new SSH connection handler process to crash. Repeated exploitation may cause each new SSH connection handler process to crash and lead to a significant amount of memory being consumed, which could introduce instability that may adversely impact other system functionality. During this event, the parent SSH daemon process will continue to function normally.

Cisco has released free software updates that address this vulnerability.

This advisory is posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20100120-xr-ssh.

Affected Products

Cisco IOS XR Software is a member of the Cisco IOS Software family that uses a microkernel-based distributed operating system infrastructure. Cisco IOS XR Software runs on the Cisco CRS-1 Carrier Routing System, Cisco 12000 Series Routers, and Cisco ASR 9000 Series Aggregation Services Routers. More information on Cisco IOS XR Software is available at http://www.cisco.com/en/US/products/ps5845/index.html.

The SSH protocol was developed as a secure replacement for the Telnet, FTP, rlogin, remote shell (rsh), and Remote Copy Protocol (RCP) protocols, which allow for remote device access. SSH varies from these older protocols in that it provides strong authentication and confidentiality and uses encrypted transactions.

The SSH server implementation in Cisco IOS XR Software contains a vulnerability that an unauthenticated, remote user could exploit to cause a denial of service condition.

The vulnerability is triggered when a new SSH handler process handles a crafted SSH version 2 packet, which may cause the process to crash. During this event, a significant amount of memory may be consumed. Repeated exploitation may impact other system functionality, depending upon the size of the available memory and the duration of attack.

Although exploitation of this vulnerability does not require user authentication, the TCP three-way handshake must be completed, and some SSH protocol negotiation must occur.

The SSH service will continue to function normally during and after an attack.

During exploitation of this vulnerability, the system may generate the following messages:

RP/0/RP1/CPU0:Jan 14 16:56:34.885 : dumper[59]: %OS-DUMPER-7-DUMP_ATTRIBUTE : 
     Dump request with attribute 407 for process pkg/bin/sshd_child_handler 
RP/0/RP1/CPU0:Jan 14 16:56:34.897 : dumper[59]: %OS-DUMPER-7-SIGSEGV : 
     Thread 1 received SIGSEGV 
RP/0/RP1/CPU0:Jan 14 16:56:34.901 : dumper[59]: %OS-DUMPER-7-BUS_ADRERR : 
     Accessed BadAddr 50199000 at PC 4a280c64 
RP/0/RP1/CPU0:Jan 14 16:56:34.906 : dumper[59]: %OS-DUMPER-4-CRASH_INFO : 
     Crashed pid = 21733716 (pkg/bin/sshd_child_handler)

This vulnerability is documented in Cisco bug ID CSCsu10574 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2010-0137.

Cisco has provided scores for the vulnerability in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this Security Advisory is done in accordance with CVSS version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding CVSS at:

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at

http://intellishield.cisco.com/security/alertmanager/cvss.

Successful exploitation of the vulnerability described in this advisory could result in a crash of the SSH connection handler process. Repeated exploitation may impact other system functionality, depending upon the size of the available memory and the duration of attack.

When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.

In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center (TAC) or your contracted maintenance provider for assistance.

This vulnerability can be addressed by applying the appropriate Software Maintenance Upgrade (SMU), per the table below. Installation of the appropriate SMU does not require a system reload. Refer to the document "Guidelines for Cisco IOS XR Software" (http://www.cisco.com/en/US/prod/collateral/iosswrel/ps8803/ps5845/product_bulletin_c25-478699.html) for additional information on Cisco IOS XR Software and SMUs.

(*) Not all Cisco IOS XR Software versions are supported by the Cisco ASR 9000 Aggregation Services Routers.

There are no workarounds for this vulnerability. Network administrators are advised to apply mitigation techniques to help limit exposure to the vulnerability. Mitigation techniques consist of allowing only legitimate devices to connect to the routers.

These access restrictions can be accomplished by using interface access control lists (ACLs) or the Management Plane Protection (MPP) feature that is available in Cisco IOS XR Software Release 3.5 and later. For information on MPP, refer to the configuration guide at http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.8/security/configuration/guide/sc38mpp.html and the MPP command reference at http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.8/security/command/reference/sr38mpp.html. Infrastructure ACLs (iACLs) are also a useful technique to mitigate potential exploitation of this vulnerability.

For more information on these mitigations, consult the Cisco Guide to Harden Cisco IOS XR Devices, which is available at http://www.cisco.com/web/about/security/intelligence/CiscoIOSXR.html.

Note that access classes in line templates applied to VTY pools are not an effective mitigation for this vulnerability.

Cisco has released free software updates that address this vulnerability. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets they have purchased. By installing, downloading, accessing or otherwise using such software upgrades, customers agree to be bound by the terms of Cisco's software license terms found at http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html , or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml .

Do not contact psirt@cisco.com or security-alert@cisco.com for software upgrades.

Customers with Service Contracts

Customers Using Third-Party Support Organizations

Customers Without Service Contracts

The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.

This vulnerability was discovered by Cisco during internal testing.

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.

This advisory is posted on Cisco's worldwide website at:

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20100120-xr-ssh

In addition to worldwide web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients.

• cust-security-announce@cisco.com
  
• first-bulletins@lists.first.org
  
• bugtraq@securityfocus.com
  
• vulnwatch@vulnwatch.org
  
• cisco@spot.colorado.edu
  
• cisco-nsp@puck.nether.net
  
• full-disclosure@lists.grok.org.uk
  
• comp.dcom.sys.cisco@newsgate.cisco.com
  

Future updates of this advisory, if any, will be placed on Cisco's worldwide website, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the above URL for any updates.

Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.